The present invention generally relates to a combustion chamber for a gas turbine engine having a combustion cowl that is surrounded by a cooling jacket through which is flowing combustion air. An open end of the combustion cowl leads into a transition piece, which is also covered by the cooling jacket, for the discharge of the combustion gases.
In a combustion chamber, the area of transition from the combustion cowl to the transition piece is critical and must be designed with particular care. The components being subjected to high running temperatures, must be able to expand radially as well as axially without interfering with each other. Furthermore, it is necessary to provide sufficient cooling for the area of transition. It is desirable to use only a relatively small amount of coolant for this cooling purpose, especially if the coolant, after its use, is to be removed from the area of transition together with the generated hot combustion gases. The known combustion chambers of the type described above do not meet these requirements.
It is therefore an object of the present invention to provide a combustion chamber of the above-defined type wherein a region of transition from the combustion cowl to the transition piece is arranged in such a manner that the various components will be able to expand freely and without touching one another. At the same time a proper amount of cooling is provided at the area of transition by a simple and controlled flow of air or some other coolant.
Another object of the present invention is to provide a combustion chamber that is simple in construction, will meet all operational requirements and has a long service life.
The present invention solves the problems of the prior art and includes at least one air gap formed between the combustion cowl and the transition piece. The at least one air gap opens into an intermediate chamber which is bordered within the area of transition from the combustion cowl to the transition piece by two throttles. The two throttles are arranged in the cooling jacket at a distance from, and opposite to each other. The throttles also serve to divide the cooling jacket into a first cooling jacket which primarily surrounds the combustion cowl and which serves to supply the air of combustion, and into a second cooling jacket which mainly surrounds the transition piece and which can be loaded with a gaseous coolant. The gaseous coolant is preferably air and is at a pressure that is higher than the pressure of the fuel gas within the area of the transition from the combustion cowl to the transition piece. The chamber formed between the throttles is in communication with the cooling jackets by way of a plurality of throttle gaps.
The air gaps formed between the combustion cowl and the transition piece allow these components to expand freely and independently from each other in radial as well as axial directions. The cooling of the area of transition is accomplished by the air and coolant flowing from the intermediate chamber through the air gap into the transition piece, with the flow of the coolant, or air respectively, being expedited by an injector effect of the fuel gas leaving the combustion cowl. Both the quantity of the air flowing from the first cooling jacket into the intermediate chamber and the quantity of the coolant flowing into the intermediate chamber from the second cooling jacket are controlled exclusively by the size of the throttle gaps. Such an arrangement makes it possible to base the dimensions of the air gap between the combustion cowl and the transition piece solely on structural aspects, and to make the gap very wide if necessary. Accordingly, there is no danger that large quantities of coolant or air will enter the transition piece through a wide air gap and thereby cool off the hot fuel gases.
The cooling jacket is separated into a first cooling jacket and a second cooling jacket. The first jacket surrounds the combustion cowl, is subjected to heavy thermal loads, and is cooled by the flow of the entire air of combustion. The second cooling jacket surrounds the transition piece, is subjected to a lesser thermal load, and is cooled only by the coolant flowing into the intermediate chamber. The separation of the cooling jacket into the first and second jackets accomplishes in a simple manner, a cooling system that is adjusted in accordance with specific thermal loads of the components.
A preferred further development of the present invention has the second throttle, which is adjacent to the second cooling jacket equipped with an annular part which is preferably flat and that embraces and is fastened to the transition piece. The annular part is engaged by an annular gap of an outer ring, with the ring forming the second throttle gap by leaving open a gap between itself and the outer wall of the cooling jacket. The ring consists of at least two annular segments which are connected with each other by a connecting ring. Such an arrangement makes it possible to adjust the dimensions of the second throttle gap by selecting outer rings of diverse thickness, while the division of the ring into two annular segments allows an easy and simple installation.
A particularly simple construction will result if the first throttle, which is adjacent to the first cooling jacket, is provided with a circular disk which is fastened to the outer wall of the first cooling jacket. The circular disk furthermore both enters the cooling jacket and ends at a distance from the combustion cowl to form the first throttle gap. However, it will be even more advantageous if the first throttle gap is formed between the combustion cowl and a cylindrical hollow piece which is supported by a circular partition both entering the cooling jacket and fastened to the outer wall of the cooling jacket.
In order to facilitate the flow of cooling air and coolant into the annular gap, it will expedient to arrange the hollow piece within the annular gap between the combustion cowl and the widened upper end of the transition piece.
Another preferred development of the invention provides that the coolant is preheated to a temperature ranging between the temperatures of the fuel gas and the air of combustion, preferably between 150.degree. C. and 300.degree. C. Such a measure leads to a considerable reduction in stresses within the area of transition.
Finally, if the combustion chamber is located directly at a gas turbine, the overall construction can be simplified by connecting the second cooling jacket with an enclosed area provided for the cooling of the gas turbine. In this way, the second cooling jacket and the enclosed area are preferably combined into one single unit.